1. Field of the Invention
The present invention relates in general to heat exchangers for use in automotive air conditioners, and more particularly to evaporators of a stack type.
2. Description of the Prior Art
In order to clarify the tasks of the present invention, two conventional stack type evaporators 1 and 1' for automotive air conditioners will be described with reference to FIGS. 24 to 26 and FIGS. 27 to 30.
One of them is shown in FIGS. 24 to 26, which is described in for example Japanese Patent First Provisional Publication 62-798 and Japanese Patent 2,737,286.
As is seen from FIGS. 24 and 25, the first conventional evaporator 1 comprises a core unit 5. Refrigerant inlet and outlet pipes 3 and 4 are fluidly connected to the core unit 5, which are held by a coupler 2. Under operation, a liquid-gaseous refrigerant is led into the core unit 5 through the inlet pipe 3 and evaporates to cool the core unit 5. With this, air flowing through the core unit 5 is cooled. Gaseous refrigerant produced as a result of the evaporation is led into the outlet pipe 4 and into a compressor (not shown). The evaporator 1 is of a so-called "stack type" which comprises a plurality of elongate flat tubes or heat exchanging elements which are stacked, each including two mutually coupled elongate shell plates. Japanese Patent 2737286 shows an alternate arrangement of two areas for the refrigerant, one being a lower temperature area mainly occupied by a liquid refrigerant and the other being a higher temperature area mainly occupied by a gaseous refrigerant. With this alternate arrangement, the evaporator can exhibit a desired temperature distribution thereon.
As is seen from FIG. 25, in assembly of the air conditioner, the evaporator 1 and a heater core 9 are arranged perpendicular to a dash panel 8 by which an engine room 6 and a passenger room 7 are partitioned, and air for conditioning the passenger room is forced to flow in the direction of the arrow "a", that is, in a direction parallel with the dash panel 8. Although not shown in the drawing, a duct is provided in the passenger room 7 to assure such air flow. That is, the evaporator 1 and the heater core 9 are installed in the duct. The coupler 2 is exposed to the engine room 6 through an opening 10 formed in the dash panel 8, so that the evaporator 1 is fluidly connected through pipes to a compressor (not shown) and a condenser (not shown) which are arranged in the engine room 6.
Nowadays, for improving air flow in the passenger room 7, there has been proposed an arrangement wherein, as is seen from FIG. 26, the evaporator 1 and the heater core 9 are arranged in parallel with the dash panel 8, and the air for conditioning the room 7 is forced to flow in the direction of the arrow "b". However, in this case, it becomes necessary to use much longer and complicated pipes as the inlet and outlet pipes 3 and 4 as is easily understood from the drawing. Of course, such arrangement brings about increase in cost of the air conditioner. Furthermore, due to usage of such complicated and longer pipes 3 and 4, the flow resistance of the refrigerant becomes marked and thus the air conditioner fails to exhibit a satisfied performance.
The other conventional stack type evaporator 1' is shown in FIGS. 27 to 30, which is described in for example Japanese Patent First Provisional Publication 62-798 and Japanese Utility Model First Provisional Publication 7-12778.
As is seen from the drawings, the second conventional evaporator 1' comprises a core unit 3'. The core unit 3' comprises a plurality of elongate flat tubes 10' (or heat exchanging elements) which are stacked, each including two mutually coupled elongate shell plates. Each elongate flat tube 10' has two mutually independent flow passages 2' and 2' defined therein. A plurality of heat radiation fins 11' are alternatively disposed in the stacked elongate flat tubes 10'. The two passages 2' and 2' defined in each flat tube 10' have upper and lower tank spaces. By connecting or communicating adjacent flat tubes 10' at the respective upper and lower tank spaces, there are formed a plurality of tank portions 4', 5' and 6'. As is seen from FIGS. 28 to 30, at one end of the core unit 3', there is provided a side tank portion 7' by which the two tank portions 4' and 4' are connected. Under operation, a liquid-gaseous refrigerant is led through an inlet pipe 8' and the inlet tank portion 5' (see FIG. 28) into the core unit 3'. The refrigerant flows in the passages 2' and 2' of the core unit 3' while evaporating to cool the core unit 3'. During this, the refrigerant flows also in the side tank portion 7'. Thus, air flowing through the core unit 3' in the direction of the arrow ".alpha." (see FIGS. 28 to 30) is cooled. Gaseous refrigerant produced as a result of the evaporation is led to an outlet pipe 9' and to a compressor (not shown).
However, the above-mentioned other conventional stack type evaporator 1' has the following drawbacks due to its inherent construction.
First, actually, the side tank portion 7' does not contribute anything to the air cooling because the portion 7' is positioned away from the air passing path. This brings about unsatisfied performance of the air conditioner.
Second, as is seen from FIG. 29, under operation of the evaporator 1', due to the nature of the gravity, the liquid-gaseous refrigerant flowing in the upper tank portions 5' and 4' of the core unit 3' is forced to feed a larger amount of refrigerant to upstream positioned flow passages 2' and 2' and a smaller amount of refrigerant to downstream positioned flow passages 2' and 2'. The amount of the refrigerant in each area of the flow passages 2' and 2' is indicated by the down-pointed arrows in the drawing. While, due to inertia of the refrigerant, the refrigerant flowing in the lower tank portions 4' and 4' of the core unit 3' is forced to feed a smaller amount of refrigerant to upstream positioned flow passages 2' and 2' and a larger amount of refrigerant to downstream positioned flow passages 2' and 2'. The amount of the refrigerant in each area of the flow passages 2' and 2' is indicated by the up-pointed arrows in the drawing. That is, the refrigerant flow rate in the core unit 3' is smaller in the inside portion than the outside portion. Thus, as is seen from FIG. 31, the core unit 3' fails to have a uniformed temperature distribution therethroughout. That is, in the drawing, the outside portions of the core unit 3' indicated by grids are forced to show a low temperature as compared with the inside portions thereof. This means that the air passing through the core unit 3' fails to have a uniformed temperature distribution, which tends to make passengers in the passenger room uncomfortable.